Requirements for PCB Assembly Drawing
Rush PCB assembles Printed Circuit Boards (PCBs) for their customers. To achieve an acceptable final product, we must faithfully follow the customer’s instructions, which in turn, must be complete and legible.
PCB assembly drawings are necessary as the person assembling the board is not the same person who has designed it. The PCB manufacturer needs the drawings to interpret how to assemble the board.
This document is an introduction to designers who have never created an assembly drawing before. It is necessary designers understand different elements of an assembly drawing and how their PCB layout tools can help in generating these documents.
Different manufacturers accept assembly drawings in several formats. It is necessary for the designer to communicate with their manufacturer to understand the form and nature of the document most suitable to them. However, there are some basic elements that all manufacturers will require when accepting assembly drawings for PCBs.
Basic Elements of Assembly Drawings
Format: Most CAD systems now generate the drawing format automatically. However, some may require the designer to create it as a separate library format. In either case, the designer will need to combine that format with their design database for building their drawing.
Outline of the Board: For fabrication, the manufacturer will require a display of the board outline of the PCB. The designer may scale the drawing to make it more presentable or show greater detail.
Mechanical Parts: The manufacturer will also require information about any mechanical part that the designer wants mounted on the PCB, along with details of the mounting hardware. Non-electrical parts may not have a regular footprint, and the designer may have to provide the drawing of the shape separately. Although some non-electrical mechanical parts may not appear on the schematic, the designer must include them in the bill of materials and in the assembly drawing.
Electrical Parts: All electrical parts that the designer wants mounted and soldered on the PCB, they must display the part shapes along with their reference designators. The designer must also list the parts in the bill of materials and reference them with their unique designators.
Notes for Assembly: Designers must offer instructions for details of basic assembly, with reference to industry specifications and standards where applicable. The notes must also contain the details and location for any special features present on the board.
Bill of Materials: This is a list of all items that the PCB will hold, along with their unique identifying reference designators. The list should also mention the manufacturer and the type number of the components.
Location of the Identification Label: PCBs often require an identification label in the form or a tag or bar code. The manufacturer will need a drawing indicating the position of the label on the board and a reference to the specific label.
Additional Drawing Views: PCBs may have components on both sides. In such cases, the manufacturer will need a view of the back side of the board along with the view of its front side. While the designer may use additional drawings for larger boards, they may include both views in a single drawing for smaller boards. For greater clarity on mounting some mechanical parts, the designer may also add drawings showing the side view of the board.
Cut-Away or Expanded Views: The designer may include expanded views of areas they want to show in greater detail for clarity of the manufacturer. They can scale the cut-away view to provide more clarity, while indicating its position on the main board with a pointer.
For further details, please contact Rush PCB.
Creating Assembly Drawings using Layout Tools
Earlier, designers had to use separate drafting tools for creating assembly drawings. However, almost all modern PCB CAD tools have the functionality to generate all the required assembly drawings in detail.
Using modern PCB CAD tools, designers can import board outlines along with parts information, and rotate, mirror, or scale them as necessary. They can compose or import assembly instructions from an external file, and add them to the drawing. It is also possible for these tools to display detailed cut-away views of the necessary area of the assembly.
After compiling all the necessary drawings, the PCB CAD tool can also convert all the drawing to the electronic format and include them with the manufacturing output files.
Rush PCB recommends designers provide good PCB assembly drawings to manufacturers to help in smooth manufacturing. Providing more details helps the manufacturer complete the assembly without confusion and delay.